Homasote 440 as a Sound Reduction Panel

Homasote 440 is a sound control panel constructed for use on subfloor, walls, and ceilings that I am hearing of being specified under resilient glue down sheet, hardwood, and LVT flooring as a sound control component. Homasote 440 is to be installed by gluing and nailing it into the wood or concrete subfloor for sound control and then the finished flooring be installed over the Homasote 440.

Homasote was a product used in the 1970’s and 80’s. in housing construction.

Per the Homasote website; Cellulose fiber comprises more than 98 percent of Homasote board and is its structural component, with nearly all board strength derived from bonding of the cellulose fibers to each other. The unique Homasote® manufacturing process begins when tons of post-consumer paper and newspaper are delivered to our plant and pulping employees separate cardboard from paper to be processed. The cardboard is bailed and resold to another recycler since its long fibers are not compatible with the Homasote®.

What I fear the most is the growth and shrinkage of this product, per the installation instructions;

During installation, leave a 3/16″ space between each panel. All panels must be spaced 3/8″ from all walls and partitions at all times. This will allow for the natural expansion and contraction of the Homasote® panels. On runs over 50’, provide 1/2″ expansion joint.

The expansion spaces described above show me that this product has the capability to expand greatly, more than particle board ever did. Applying a 1/4” underlayment over a product that is going to grow/shrink like this is going to result in staple popping and loose underlayment.

Below are the installation requirements for the Homasote 440, which in new construction will rarely be met:

Temperature and humidity conditions closely approximating those which will exist when building is occupied shall be maintained before, during, and after the application of panels. Installation shall not be made when building is excessively dry, cold, hot or damp. All panels shall be removed from plastic covered units and separated not less than 24 hours prior to installation to allow material to acclimate.

Homasote Installed to Wood Sub-floor

Attach the 1/4” plywood over Homasote panel, assuring that plywood joints do not coincide with the Homasote joints. Follow the plywood manufacturer’s recommended method and pattern of attachment, making sure that mechanical fasteners are of sufficient length to penetrate through Homasote panel and into wood sub-floor a minimum of 1/2″.

They also state you may install Vinyl, Linoleum, Glue-down Wood Strip Flooring, Wood Parquet, and Glue down Carpet directly over the Homasote 440;

Alternative application without 1/4” underlayment

Apply joint filler such as Sikaflex® 1C SL, Sonneborn® NP1 or Dash Patch® to fill gaps in the Homasote Panels. For further information see:“Suggested Joint Fillers” on the “Installation Instructions” page.

If Using Dash Patch®

Apply dash patch a little over the height of the joint; allow material to set following manufacturer’s installation instructions and then sand joints down flush with 440 Sound Board. The Homasote is now ready to accept finished flooring.

The key here is in the third bullet point above, Install finish floor covering in strict accordance with manufacturer’s instructions. I have researched many flooring websites, and have not seen any reference to Homasote 440 being an acceptable subfloor or underlayment for resilient flooring. I also called Armstrong, Flexco, Mannington, Roppe, and Tarkett and none of them recommended Homasote 440 as an acceptable subfloor or underlayment for their products.

I called Ultraply XL, an underlayment board manufacturer that JJ Haines sells and they said they would not warrant their underlayment installed directly over Homasote 440.

Also, per the American Plywood Association, plywood underlayments are to be installed directly to the subfloor, not a product used between the underlayment and subfloor.

My other concern when installing a 1/4″ plywood over the Homasote 440, is that with most sound reduction materials, no fasteners should protrude the sound reducing material as they will transmit the sound down through the fastener. On a 4′ x 4′ sheet of underlayment, there will be at least 192 staples used to install it. A room 12′ x 12′ will have 1728 staples used to staple the underlayment down. That is a lot of fasteners that can transport sound down through the sound reducing material.

The other point is that I can find no compressive strength number for this product. Generally for floor covering, a fill or topping should have a compressive strength of 3500 psi or better.

Bottom line is, that there are other sound reduction products on the market that flooring manufacturers approve of and warrant their products over.